1. Field of the Invention
This invention relates to a communication terminal device, a base station, and a communication method with which bidirectional communication is performed by applying different frequencies for transmission and reception.
2. Description of the Related Art
Conventionally, voice over internet protocol (VoIP) that utilizes an internet protocol (IP) to realize an inexpensive voice call system via a router has been used. It is under study to realize VoIP also in a mobile communication system. Applying frequency division duplexing (FDD), which enables bidirectional communication by applying different frequencies for transmission and reception, for this VoIP is also under study.
In VoIP, a mobile communication system is proposed that receives down link (DL) data and transmits up link (UL) data periodically and shifts to a sleep mode when neither reception of the DL data (reception signal) nor transmission of the UL data (transmission signal) is performed.
FIG. 20 is a diagram of an outline of a scheduler scheme in a conventional mobile communication system. The horizontal axis, time, shown in FIG. 20 is a time axis. DL 101 is a time period when the communication terminal receives the DL data and UL 102 is a time period when the communication terminal transmits the UL data.
A blank period 103 is a time period when the communication terminal is in a sleep mode (an energy-saving standby mode) (hereinafter, “sleep mode period 103”). As shown in FIG. 20, in the conventional communication system, a communication interval T of the DL data reception and of the UL data transmission is notified to the communication terminal, and during the sleep mode period 103 which is the period other than the DL 101 and the UL 102, the communication terminal shifts to the sleep mode (for example, Publication PCT Application No. 2003-503982).
However, in the conventional technology described above, timing of the DL 101 may coincide with that of the UL 102 (the DL 101 and the UL 102 overlap each other) or may not, dependent on the timings of the DL 101 and the UL 102. When the timing of the DL 101 coincides with that of the UL 102, the DL 101 and the UL 102 shown in FIG. 20 overlap each other, and the sleep mode period 103 becomes longer.
On the other hand, in the example shown in FIG. 20, there is a time difference Δt between the DL 101 and the UL 102. In this case, because the communication terminal is operating during the DL 101 and the UL 102 and thus the sleep mode period 103 becomes short, there is a problem that power consumption becomes larger than when the timings of the DL 101 and the UL 102 coincide.
Moreover, training periods for the DL data reception and for the UL data transmission, respectively, are necessary just before the DL 101 and the UL 102, and the communication terminal is also operating during the training periods. When the timings of the DL 101 and of the UL 102 coincide with each other, the training periods for the DL 101 and for the UL 102, respectively, also coincide with each other. On the other hand, when the timings of the DL 101 and of the UL 102 do not coincide with each other, the training period becomes longer than when the timings of the DL 101 and of the UL 102 coincide with each other, and the operating time of the communication terminal becomes longer. This causes a problem to increase power consumption.